Interpretive Summary: This work characterized a novel green composite from alternate oilseed coproducts and poly(lactic acid) fabricated by twin-screw extrusion and injection molding. The composites showed similar mechanical properties to some conventional polymer composites, and are biodegradable and competitive in cost with comparable non-sustainable petroleum based products currently in the marketplace. The manuscript also discusses several technical issues such as the effect of the filler/matrix ratio on the structural and mechanical properties of resultant composites and provides useful information for the studies of other natural fiber-reinforced biobased polymer composites. The current study presents a new way to utilize agricultural by-products for the future profitability of the agriculture industry.

Technical Abstract:
Poly(lactic acid), PLA, is a biodegradable polymer made from renewable resources with similar mechanical properties to polypropylene. PLA is more expensive than petroleum-based plastics, and the use of low-cost fillers as extenders is desirable. Agricultural co-products of the alternative oilseed crops, cuphea(C), lesquerella(L) and milkweed(M), were collected after the oil was recovered. PLA and various levels of coproduct (0-45% w/w) were compounded by twin-screw extrusion and injection molded. As coproduct content increased, tensile strength for all PLA composites decreased consistent with the Nicolais-Narkis model. PLA-C exhibited increased stiffness. In contrast, the modulus of PLA-M & PLA-L decreased slightly. Unexpectedly, PLA-M showed extensive stress-cracking under tensile stress and exhibited an elongation value 50% to 200% greater than the PLA control. Acoustic emission showed ductile behavior of the PLA-M composite.